Friday, January 11, 2013

I finally got an IC decapsulation setup up and running in my new lab. Been a while but I'm back in business :)

Now that I have a proper (homebrewed) fume hood decapping is a lot easier and safer. No fumes to breathe, and a nice thick sash between me and the beaker of hot acid if something goes wrong. That said, I still wear goggles, gloves, and a lab coat as per SOP.

For the new process I am using sulfuric acid as it's much cheaper than nitric. (Concentrated sulfuric of an acceptable quality can be purchased as a drain cleaner, while nitric must be mail-ordered with special hazmat shipping fees). The downside is that sulfuric cannot be used for live decapsulation (at least not easily) since it takes so long. For bare-die decaps it's by far the most cost-effective option, though.

The first step, as is usual for bare-die decaps, is to put them in a beaker of acid, cover with a watch glass or petri dish to slow down evaporation losses. and heat.

View through the sash of my fume hood as the acid warms up

Pure sulfuric acid starts out a pale yellowish to clear but turns reddish-brown and then black from carbon particles as the decap proceeds. Drain-cleaner grade will normally be stored in a plastic bottle and have absorbed some organics already, causing discoloration.

Close up of beaker on the hot plate

As the decap progresses the beaker fills up with acid fumes and the acid turns darker.

Later in the decap

At this point all that has to be done is to leave the chips to cook for a while. I was running at only around 100C (150-200 is more common) so it took an hour or two.

Before I get to the results, a warning as to what you're dealing with here. While pouring the used acid off into another beaker to pull the dies out with tweezers, I spilled a drop on a kimwipe I had in the hood. This was the result:

H2SO4 + organics = bad

In this picture I was decapping a pair of FTDI FT232RL USB-serial adapters as well as a MAX232. The MAX232 wasn't left in quite long enough so I'm going to need to clean it with more acid later on. Here's a pic of the FT232R: